The present invention relates in general to condensation, and, more particularly, to condensation of zirconium tetrachloride and/or hafnium tetrachloride to a free-flowing solid.
In the production of zirconium, zirconium is recovered as a co-product from zirconium sand. Broadly, the recovery process includes the steps of separating rutile and ilmenite and zirconium in an ore dressing step from zirconium sand. The process also includes: ball milling; sand chlorination, feed makeup; separation; precipitation; calcination; pure chlorination; reduction; distillation; a breakup process; crushing; blending; pressing; beam welding; melting into ingots; machining; and fabricating a wrought product from the final machine ingots. The production of hafnium is similar to the steps above and variations thereof required for the production of hafnium are known to those skilled in the art.
Fluid bed condensers are often used in at least one step of the just-described production process. In at least one of these condensers, zirconium tetrachloride and hafnium tetrachloride is condensed to free-flowing solids. The condenser used often includes a water cooled jacket. It has been found that solid material builds up in and adjacent the inlet used to conduct vapor into the vessel. The build up of solid in and at the inlet presents problems. The influx is reduced, and, if the outlet is not cleared, eventually influx is stopped.
For example, in the production if zirconium tetrachloride, zirconium tetrachloride vapor enters a condenser via an intake pipe, and is kept in a vapor state until it enters the fluidized bed condenser by heaters surrounding the intake pipe. Caking of zirconium tetrachloride around the entrance of the intake pipe to the condenser is a phenomena caused because heat applied to the vapor by a heater used on the intake pipe nullifies the cooling effect of a cooling jacket surrounding the condenser. The heater causes a local overheating of the cooling fluid, which surrounds the condenser at the entrance opening. As a result of this localized overheating, the zirconium tetrachloride cakes around the intake pipe opening. This caking continually builds as new zirconium tetrachloride vapor condenses on the zirconium tetrachloride particles already attached to the side of the condenser adjacent the intake pipe opening into the condenser. Large particles result, of the nature of sintered products at the opening, thus blocking the inflow of zirconium tetrachloride vapor. This phenomena does not occur in other parts of the condenser as the water cooling in parts of the condenser remote from the aforementioned heaters are effective to prevent attachment of zirconium tetrachloride to the surface of the condenser.